1. Field of the Invention
The present invention generally relates to a method and apparatus for lining pipe. In particular, the invention relates to lateral connections that are used to compliment relining of an existing sewer line or similar conduit.
2. Description of the Prior Art
Liners for pipe, such as that used in sewer pipelines, are often applied as the pipe ages to extend the life of the original fixture. Means for lining pipe are well known in the art. One such method is disclosed by LeDoux et al. in U.S. Pat. No. 4,985,196. This method employs a thermoplastic liner which is initially formed in a cylindrical shape with a diameter slightly larger than the internal diameter of the pipe. The liner is temporarily deformed at an elevated temperature to a reduced cross section, preferably U-shaped, to reduce its overall cross-sectional dimension and facilitate insertion into the pipe to be lined. After insertion, the liner is re-heated and pressurized so that shape memory characteristics of the thermoplastic material cause the liner to return to its original cylindrical shape. The liner is further adapted to conform to the interior surface of the pipe by means of increasing pressure within the liner in two stages. Additionally, an expansion pig may be employed to ensure even more exact conformance.
Other methods, which also employ liners, are discussed in U.S. Pat. No. 4,867,921 by Steketee, Jr. and U.S. Pat. No. 4,861,634 by Renaud. The Steketee, Jr. patent suggests that such a liner may be restored to a cylindrical shape by plugging the ends of the liner and pressurizing the liner with an expanding material such as live steam or hot water. It also teaches the use of an apparatus comprising a mandrel having a heating means therein which may be drawn through the liner to expand the liner to the desired diameter.
Still another recommended method, disclosed in the Steketee, Jr. patent, involves flushing hot water or steam down the original pipeline alongside the folded liner until the desired temperature is achieved at the downstream end. Once the desired temperature is reached, the liner is pressurized with hot water and expanded under pressure to fit.
The Renaud patent discloses a method of lining ducts wherein a sleeve permeable over at least a part of its thickness to a heat hardenable resin, such as an epoxy resin, is introduced into the duct. The sleeve is able to enlarge its section under the action of a pressure exerted on its internal wall and able to adapt its section to that of the duct without the composite material for such sleeve undergoing an elastic or plastic deformation. The internal pressure is exerted via an inflatable balloon until the external wall of the sleeve is applied against the internal wall of the duct, and it is held in place until the resin hardens, at which time the balloon is deflated and removed. The surface of the balloon for this apparatus may include a heating element or elements in the form of metal wires or strips to aid in curing the resin. Heating is provided by electric means.
Unfortunately, current pipe lining methods are not a complete solution to the problems posed by a deteriorating pipeline. When sewer lines and similar conduits are relined, the newly emplaced liner will normally cover lateral entrances for smaller pipes which feed into the freshly lined pipe. As a result, holes must be cut in the liner to reexpose these entrances. Holes cut into the liner, however, will permit waste and effluent to enter the space created between the new liner and old pipeline at the point where the lateral line feeds in. The possible results from this entry include separation of the liner from the pipeline, escape of effluents and further decay of the original pipeline. This could, in turn, leave spaces between the liner and the surface of the original pipeline which would promote decay and freeze-thaw failures for the liner.
Limited efforts toward solving this problem have been made. KWS.multidot.VSH leidingrenovatie v.o.f. has recently developed a method for emplacing a thermoplastic protective lining at a laterally intersecting pipeline junction. The method involves cutting a hole in the liner of a relined main pipeline to expose a lateral opening and placing an annular thermoplastic lining which has a mastic on the outside diameter within the opening. The annular lining is then expanded and sealed to the liner of the main pipeline by heating and expanding the lining thereby squeezing the mastic to form a seal with the aid of an axially placed expandable heated mandrel.